BOSTON, MASSACHUSETTS. A deficiency of folate (folic acid) prior to and during preganancy increases the risk of giving birth to a baby with neural tube defects. A lack of folate has also been linked to an increased risk of cardiovascular disease. Now researchers at the Harvard Medical School report that women with a high folate intake decrease their risk of developing colon cancer by as much as 75 per cent. Their study which began in 1980 involved 88,756 female nurses. The nurses completed food frequency questionnaires in 1980, 1984, 1986, and 1990 and also provided information about their use of vitamins, lifestyle factors, and family history which could affect their risk of colon cancer. During the period from 1980 to June 1994 442 of the women developed colon cancer. Statistical analysis showed that women who had supplemented with multivitamins containing folic acid (>400 micrograms/day) for 15 years or more had a four times lower risk of colon cancer than did women whose daily intake had been 200 micrograms/day or less. This association remained true after adjusting for age, family history of colorectal cancer, aspirin use, smoking, weight, degree of physical activity, and intake of red meat, alcohol, methionine and fiber. Adjustment for intake of vitamin-A, vitamin-C, vitamin-D, vitamin-E and calcium did not alter the folate/colon cancer correlation. However, it was clear that the benefits of folate became evident only after 15 years or more of supplement use although smaller statistically non-significant risk reductions were noted after five years. The risk reduction associated with folate supplementation was particularly evident among women with low methionine levels. Folate is essential in the regeneration of methionine and a deficiency may lead to abnormalities in DNA synthesis and repair - mechanisms which may influence the development of colon cancer. The researchers found a significantly stronger correlation between the intake of folate from supplements and a reduced colon cancer risk than between the intake of dietary folate and reduced risk. They ascribe this to the relatively low bioavailability of folate from food sources and conclude that long term use of multivitamins containing folic acid reduces the risk of colon cancer in women. Other studies have shown that folic acid supplementation also reduces colon cancer risk in men. NOTE: Certain birth control pills and drugs such as methotrexate can markedly lower folate levels in the body.
Giovannucci, Edward, et al. Multivitamin use, folate, and colon cancer in women in the Nurses' Health Study. Annals of Internal Medicine, Vol. 129, October 1, 1998, pp. 517-24